The present invention relates to image forming apparatuses having a waste toner container to collect and store toner remaining on the surface of an image bearing member after a transferring step.
In electrophotography image forming apparatuses, an electrostatic latent image is formed on the surface of an image bearing member such as a photoreceptor drum or a transfer belt, subsequently a toner image is formed thereon, and thereafter the toner image is transferred from the image bearing member to a sheet. Toner not transferred to the sheet but remaining on the surface of the image bearing member is collected in a waste toner container via a cleaning unit or the like for storage.
As the number of sheets subjected to image formation (hereinafter called the number of image-forming sheets) increases, the amount of waste toner in the waste toner container increases and the waste toner container becomes full in due time. If waste toner is further collected in the waste toner container in a full-capacity state, a problem will arise, such as overflow of waste toner from the waste toner container. To avoid this, conventional image forming apparatuses enter a disabled state when the waste toner container becomes full, and issue an alarm to urge a user to replace the waste toner container.
Some of the image forming apparatuses are configured for smooth replacement of the waste toner container so as to issue an alarm before entering the disabled state and when the waste toner container is approaching replacement time (for instance, see JP 2004-101667 A, called Patent Document 1).
The conventional techniques including Patent Document 1, however, sometimes fail to detect the amount of waste toner in the waste toner container precisely. For instance, in the configuration detecting the weight of waste toner using a spring provided below the waste toner container, precise weight cannot be detected in some cases because of variations of spring accuracy or imbalance in toner distribution. In another case of detecting the amount of waste toner in the waste toner container on the basis of image formation information such as the number of image-forming sheets, the amount of waste toner even for the same number of image-forming sheets varies with the frequency of color printing and monochrome printing, a print density, a type of an image printed and the like.
Such a failure results in the difficulty to detect an appropriate replacement time for the waste toner container, sometimes causing the overflow of waste toner from the waste toner container or unnecessary replacement of the waste toner container in spite of enough space left in the waste toner container.
It is an object of the present invention to provide an image forming apparatus capable of detecting an appropriate replacement time of a waste toner container.